Alpha-olefins, especially those containing about 6 to about 20 carbon atoms, are important items of commerce, with about 1.5 million tons reportedly being produced in 1992. The .alpha.-olefins are used as intermediates in the manufacture of detergents, as monomers (especially in linear low density polyethylene), and as intermediates for many other types of products. As a consequence, improved methods of making these compounds are of interest.
Most commercially produced .alpha.-olefins are made by the oligomerization of ethylene, catalyzed by various types of compounds, see for instance B. Elvers, et al., Ed. Ullmann's Encyclopedia of Industrial Chemistry, Vol. A13, VCH Verlagsgesellschaft mbH, Weinheim, 1989, p. 243-247 and 275-276, and B. Cornils, et al., Ed., Applied Homogeneous Catalysis with Organometallic Compounds, A Comprehensive Handbook, Vol. 1, VCH Verlagsgesellschaft mbH, Weinheim, 1996, p. 245-258. The major types of commercially used catalysts are alkylaluminum compounds, certain nickel-phosphine complexes, and a titanium halide with a Lewis acid such as AlCl.sub.3. In all of these processes significant amounts of branched and/or internal olefins and/or diolefins, are produced. Since in most instances these are undesired, and often difficult to separate from the desired linear .alpha.-olefins, minimization of these byproducts is sought.